The present invention relates to a deflection-coil system for multibeam color-picture tubes wherein, for dynamic convergence correction, a 45.degree./45.degree. four-pole field is superimposed on the deflection fields with component windings of the deflection coils.
This 45.degree./45.degree. four-pole field is needed to achieve convergence over the entire screen, as is described in detail in the Journal "Funkschau", 1976, No. 1, Ro 64, pages 21-22. It is commonly produced by four additional toroidal windings wound around the deflection-coil core, as is described, for example, in German Pat. No. 2,031,837 for both delta-gun and inline arrangements.
45.degree./45.degree. four-pole fields provided by these additional toroidal windings fulfil the requirements imposed on them in terms of convergence correction quite satisfactorily.
However, the four additional windings occupy much winding space. This limits the number of turns of a vertical deflection coil in the form of a toroid and, thus, reduces the attainable vertical deflection sensitivity. If horizontal deflection is produced by a saddle coil, and vertical deflection by a toroidal coil, two of the four additional windings must be located at points where the coil core is divided prior to assembly, which entails winding problems.
Integration of the four auxiliary windings into the actual deflection windings is described in German Pat. No. 2,341,646. There, however, both the horizontal and the vertical deflection coil are toroids, so that it is possible to produce the 45.degree./45.degree. four-pole field by means of the four toroidal-coil halves if the latter are suitably wired.